This invention concerns a water level sensor, particularly keeping a water level at a preset height in a tank for preventing the tank from burning owing to no water therein.
Conventional drink water dispensers are provided with a tank disposed with a water level sensor to prevent the tank from burning. As the tank keeps water therein at a certain temperature or boils it, and if water in the tank becomes too little or is used up, the tank will be burned unless a water level sensor senses the water level and activates to turn off electric power.
A conventional water level sensor shown in FIG. 5 includes a magnetic tube 11, a sleeve 14 and a float 15 combined together. The magnetic tube 11 has straight projections 111 on an outer surface, an annular groove 112 for an elastic ring 113 to fit therein for keeping the sleeve around the magnetic tube 11. A magnetic switch 12 is disposed inside the magnetic tube 11 and connected with a power cord 13.
The sleeve 14 is a hollow tube, having straight grooves 141 in an inner surface, a vertical bar 142 formed to extend up from a center portion having straight projections 143 on an outer surface, an annular groove 144 near an upper end for an elastic ring 145 to fit therein for keeping the float 15 combined with the vertical bar 142.
The float 15 is shaped cylindrical, having a lower end open, an inner annular wall 150 defining a center hole for the vertical bar 142 to extend therein, two straight grooves 151 in the inner surface of the inner annular wall, an annular cavity 152 defined between the inner annular wall 150 and an outer annular wall, several annular engage members 153 on a lower end surface for fitting annular rings 16 therein, and then gaskets 17, 18 fitted around an inner surface and an outer surface and closed with a bent cap 19 on the lower open end of the float 15.
In using, referring to FIG. 6, as the water level sensor 1 is fixed with a side wall of a tank at the magnetic tube 11, and the sleeve 14 is combined with the magnetic tube 11 by means of the straight grooves 141 engaging the straight projections 111, and the elastic ring 113 fitted in the annular groove 112 to position the sleeve 14 in place. Then the vertical bar 142 is inserted in the float 15, letting the straight grooves 151 engaging the straight projections 143. Then the elastic ring 145 is fitted in the annular groove 144 to limit the position of the float 15, which moves up and down according to a water level. When the water level is too high or low, the float 15 moves also to activate the magnetic switch 13 to cut off the power coming from the power cord 13. Thus the tank can be prevented from burning with no water therein.
The conventional water level sensor has too many components and thus its cost is comparatively high. Besides, when the water level falls to a preset certain location, the magnetic ring 16 and the magnetic switch 12 produce induction to activate the power to be cut off. However, the magnetic switch 12 is separated from the magnetic ring 16 by the thickness of the magnetic tube 11 and the inner annular wall 150 so that magnetic force may sometimes not be transmitted well, causing induction impossible to be produced and failing to cut off the power even if the water level should fall down below the preset certain level.